Targeted irradiation of testis by carbon ion microbeam formed testis-ova in adult male medaka (Oryzias latipes)

Gamma-ray irradiation promotes the formation of testis-ova in p53-deficient medaka (Oryzias latipes) and this finding suggests the possible involvement of p53 in sex differentiation in medaka [1]. Since administration of female hormone, estrogen, induces testis-ova in male fish, irradiation may disturb the hormonal balance and induce the testis-ova. To investigated whether the involvement of the hormonal imbalance by irradiation in the testis-ova induction, we put a 5 mm-thick acrylic plate for shield and separately irradiated the head and body of adult male fish using the carbon ion beam in Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), QST[2]. Whereas testis-ova were not observed in the testis of the head-irradiated males 14 days after irradiation, testis-ova were observed in the body-irradiated males, demonstrating that direct irradiation of the testis is required to induce testis-ova. To confirm this finding, we used a collimated carbon ion microbeam irradiation (2 Gy and diameter of 250 µm) in TIARA to conduct targeted irradiation of p53-deficient male medaka testis. Seven days after irradiation, we found that testis-ova were induced only in the cyst of type A spermatogonia (Ga) that was expected to be located in the path of the microbeam. These results indicate that direct irradiation of p53-deficient testis induced abnormal differentiation of Ga to testis-ova and that microbeam is highly applicable to investigate the irradiation-induced cellular response in vivo.第23回小型魚類研究